“We rightly shudder at promiscuous or misplaced apostrophization, for instance when a family named Bennett puts up a sign in front of their house that says The Bennett’s, thereby suggesting that there is only one, self-aggrandizing Bennett. (The Bennetts or The Bennetts’ would do.) But sometimes we hear that apostrophes should never be used in a plural. For instance in The Alphabet Abecedarium, by RIchard A. Firmage: ‘For clarity I have occasionally inserted the mark (usually with vowels, e.g.,O’s) although my preference is to be technically correct and omit them.’ Hey, Richard, don’t apologize. It’s helpful to use an apostrophe in the plural of a letter or number: T’s, w’s, 9’s. What is the reader to make of Ts and ws or even 9s? That last looks like nine shillings, or a typo. If you were to write, ‘There are four is in Mississippi,’ or for that matter, ‘four ss in Mississippi’—you see what I mean. ‘Four i’s and four s’s’ is the only way to go.”